An important process for the production of acetic acid is the carbonylation of an alkyl alcohol, especially methanol, and reactive derivatives thereof, with carbon monoxide in a liquid reaction medium. In commercial processes, the carbonylation rate of reaction is strongly dependent on water concentrations, and thus it is important to maintain water levels in the reaction mixture during the production of acetic acid within controlled ranges to maintain high reaction rates. In some commercial processes, water is added to exert a beneficial effect upon the reaction rate and a water concentration of 14 to 15 wt. % are maintained as described in U.S. Pat. No. 3,769,329. This is commonly referred to as a “high water” carbonylation process. In other “low water” carbonylation process, as described in U.S. Pat. Nos. 5,001,259, 5,026,908, and 5,144,068, water concentrations lower than 14 wt. % are used. In the low water carbonylation process, water may be controlled in by optimizing the reaction conditions based on methanation reaction and water gas shift reaction, as described in U.S. Pat. No. 7,005,541. Once water balance is controlled, either in a high or low water carbonylation process, when purifying acetic acid the water is continuously returned to the reaction medium to maintain the water balance. Upsets in the water balance may adversely affect the carbonylation reaction rate.
Integrated processes for forming ethanol from methanol, preferably through an acetic acid intermediate have been proposed in the literature. Generally, the acetic acid intermediate production produces glacial acetic acid that has less than 1500 wppm water by separating water from the acetic acid. For example, U.S. Pat. No. 7,884,253 discloses methods and apparatuses for selectively producing ethanol from syngas. The syngas is derived from cellulosic biomass (or other sources) and can be catalytically converted into methanol, which in turn can be catalytically converted into acetic acid or acetates. The ethanoic acid product may be removed from the reactor by withdrawing liquid reaction composition and separating the ethanoic acid product by one or more flash and/or fractional distillation stages from the other components of the liquid reaction composition such as iridium catalyst, ruthenium and/or osmium and/or indium promoter, methyl iodide, water and unconsumed reactants which may be recycled to the reactor to maintain their concentrations in the liquid reaction composition.
EP2060553 discloses a process for the conversion of a carbonaceous feedstock to ethanol wherein the carbonaceous feedstock is first converted to ethanoic acid, which is then hydrogenated and converted into ethanol.
U.S. Pat. No. 4,497,967 discloses an integrated process for the preparation of ethanol from methanol, carbon monoxide and hydrogen feedstock. The process esterifies an acetic anhydride intermediate to form ethyl acetate and/or ethanol.
U.S. Pat. No. 7,351,559 discloses a process for producing ethanol including a combination of biochemical and synthetic conversions results in high yield ethanol production with concurrent production of high value co-products. An acetic acid intermediate is produced from carbohydrates, such as corn, using enzymatic milling and fermentation steps, followed by conversion of the acetic acid into ethanol using esterification and hydrogenation reactions.
As such, the need remains for improvements in the integration of acetic acid production and ethanol production.